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Definition: free software

(2) Software that is free of restrictions and which may be free of charge. Free software licenses grant users the freedom to use it for any purpose, study and change the source code and copy and redistribute the software with or without modifications. Free software must come with source code or provide access to it, while the freedom to redistribute includes the right to give away copies gratis as well as sell copies. For the complete, official definition, visit www.gnu.org/philosophy/free-sw.html.

Occasionally, free software comes from proprietary products that were liberated by their developers; for example, the proprietary Netscape Web browser was later turned into the free software Mozilla and Firefox browsers (see Mozilla). However, most free software is intentionally written to be free, the most notable of which is the GNU/Linux operating system (see Linux).

Free Means Freedom, Not Free of Charge
When used in the context of this definition (not #1 above), without a doubt, the "free" in free software can be misleading. Although a huge amount of free software is indeed free of charge, and most developers of free software are volunteers, there is also a great amount that is not. For example, many distributions of the GNU/Linux system are paid for by the customer (see Linux distribution). Therefore, since free software can be commercial, the notion of free software should be contrasted with "proprietary software," not "commercial software."

Copyleft Licenses
Some free software licenses are copyleft licenses, which states that anyone redistributing the software does so under the same license and also includes the source code. The dominant copyleft license is the GNU GPL (see GNU General Public License). However, there are also non-copyleft free software licenses that do permit distribution of proprietary versions.

Free Software vs. Open Source
The difference is philosophy. Strongly influenced by its founder Richard Stallman, the Free Software Foundation extols the virtues of free software as an ethical movement, vitally necessary for the advancement of society. Open source was derived from the free software movement, but focuses on practical benefits without touting moral issues. In fact, most open source licenses are free software licenses, but some are too restrictive to qualify. See free software movement, GNU, Linux, GNU/Linux and open source.